As production looms closer for Andrew Niccol’s (In Time) adaptation of the Stephanie Meyer sci-fi novel The Host, the director continues to fill out his cast. SaoirseRonan is onboard as the protagonist Melanie, a young woman whose body is invaded by an alien name Wanderer. Diane Kruger (Inglorious Basterds) is now apparently in talks to play The Seeker. In the world of the film, a parasitic alien species is nearly finished wiping out the human population by taking over the consciousness of each person. A soul named Wanderer is attempting to take control of Melanie’s consciousness, but faces strong opposition by what remains of the girl. Hit the jump for more.

The Seeker is charged with overseeing the conversion of Melanie, and keeps a close eye on the girl as she knows that the conversion of the rebel will lead to the eradication of the rebel movement. Max Irons plays a young man in love with Melanie and Jake Abel plays a young man in love with Wanderer, with William Hurtin talks to play a rebel leader. Kruger was previously a candidate for a lead in the ambitious untitled Tom Cruise sci-fi pic at Universal, but she dropped out of consideration in favor of The Host.

Deadline’s report on the matter also mentions that the movie is being set up as the first in a trilogy, despite the existence of only one book. Meyer has previously stated that she plans on writing two sequels to the novel, but there’s no word on when those might come to fruition. Nevertheless, The Host is set for release on March 29th, 2013.

Here’s the synopsis for the novel:

Melanie Stryder refuses to fade away. The earth has been invaded by a species that take over the minds of human hosts while leaving their bodies intact. Wanderer, the invading “soul” who has been given Melanie’s body, didn’t expect to find its former tenant refusing to relinquish possession of her mind.

As Melanie fills Wanderer’s thoughts with visions of Jared, a human who still lives in hiding, Wanderer begins to yearn for a man she’s never met. Reluctant allies, Wanderer and Melanie set off to search for the man they both love.

Featuring one of the most unusual love triangles in literature, THE HOSTis a riveting and unforgettable novel about the persistence of love and the essence of what it means to be human. [Amazon]